A PHYSICALLY-BASED MODEL FOR THE TOPOGRAPHIC CONTROL ON SHALLOW LANDSLIDING

A model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near-surface throug h flow and slope stability models. The hydrologic model TOPOG (O'Lough lin, 1986) predicts the degree of soil saturation in response to a ste ady state rainfall for topographic elements defined by the intersectio n of contours and flow tube boundaries. The slope stability component uses this relative soil saturation to analyze the stability of each to pographic element for the case of cohesionless soils of spatially cons tant thickness and saturated conductivity. The steady state rainfall p redicted to cause instability in each topographic element provides a m easure of the relative potential for shallow landsliding. The spatial distribution of critical rainfall values is compared with landslide lo cations mapped from aerial photographs and in the field for three stud y basins where high-resolution digital elevation data are available: T ennessee Valley in Marin County, California; Mettman Ridge in the Oreg on Coast Range; and Split Creek on the Olympic Peninsula, Washington. Model predictions in each of these areas are consistent with spatial p atterns of observed landslide scars, although hydrologic complexities not accounted for in the model (e.g., spatial variability of soil prop erties and bedrock flow) control specific sites and timing of debris f low initiation within areas of similar topographic control.